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Location of ovules inside a Helleborus foetidus flower. In seed plants, the ovule is the structure that gives rise to and contains the female reproductive cells. It consists of three parts: the integument, forming its outer layer, the nucellus (or remnant of the megasporangium), and the female gametophyte (formed from a haploid megaspore) in its center.
The egg cell or ovum (pl.: ova) is the female reproductive cell, or gamete, [1] in most anisogamous organisms (organisms that reproduce sexually with a larger, female gamete and a smaller, male one). The term is used when the female gamete is not capable of movement (non- motile ).
Macrolecithal eggs are only found in selected representatives of two groups: Cephalopods and vertebrates. [7] [22] Macrolecithal eggs go through a different type of development than other eggs. Due to the large size of the yolk, the cell division can not split up the yolk mass.
An oocyte (/ ˈ oʊ ə s aɪ t /, oöcyte, or ovocyte is a female gametocyte or germ cell involved in reproduction. In other words, it is an immature ovum, or egg cell. An oocyte is produced in a female fetus in the ovary during female gametogenesis. The female germ cells produce a primordial germ cell (PGC), which then undergoes mitosis ...
On the deep surface of the inner cell mass, a layer of flattened cells, called the endoderm, is differentiated and quickly assumes the form of a small sac, called the yolk sac. Spaces appear between the remaining cells of the mass and, by the enlargement and coalescence of these spaces, a cavity called the amniotic cavity is gradually developed.
The blastula (from Greek βλαστός (blastos meaning sprout)) is a hollow sphere of cells known as blastomeres surrounding an inner fluid-filled cavity called the blastocoel. [1] [2] Embryonic development begins with a sperm fertilizing an egg cell to become a zygote, which undergoes many cleavages to develop into a ball of cells called a ...
The chalaza (/ k ə ˈ l eɪ z ə /; from Ancient Greek χάλαζα (khálaza) 'hailstone'; pl.: chalazas or chalazae / k ə ˈ l eɪ z i /) is a structure inside bird eggs and plant ovules. It attaches or suspends the yolk or nucellus within the larger structure.
M phase See mitosis. macromolecule Any very large molecule composed of dozens, hundreds, or thousands of covalently bonded atoms, especially one with biological significance. . Many important biomolecules, such as nucleic acids and proteins, are polymers consisting of a repeated series of smaller monomers; others such as lipids and carbohydrates may not be polymeric but are nevertheless large ...